Measurement of quality in pediatric cardiac surgery: understanding the threats to validity.

The initiation of pay for participation and the expected move to pay for performance have increased the stakes for and amplified the importance of valid quality measures. Assessing the outcomes of clinical care is difficult and relies on the methods of observational epidemiology. Because pediatric cardiac surgery operations are performed relatively infrequently at individual hospitals and mortality rates are generally low, understanding the limitations inherent in the design of observational studies is imperative. Detailed study of the processes of care by multicenter, multidisciplinary quality improvement initiatives may augment national databases in improving outcomes.